Diamond is a wide-bandgap semiconductor with a bandgap of 5.5 eV. The surface of diamond, when terminated with hydrogen atoms, is known to be an excellent electron emitter. Hydrogen atoms on the surface lead to a property known as negative electron affinity (NEA), in which the conduction band lies above the so-called “vacuum level,” which is the energy of a free electron in space. Whereas with conventional semiconductors electrons are bound inside the material by several electron-volts even when illuminated with light, when electrons are excited to the conduction band of hydrogen-terminated diamond, the electrons have no barrier to emission. Consequently, excitation of hydrogen-terminated diamond with light more energetic than its bandgap leads to facile electron emission. Electron emission can also be stimulated electrically by using an applied electrical potential through a process known as field emission. Electrons emitted from hydrogen-terminated diamond via light or applied electrical potential are capable of inducing a variety of reduction reactions (e.g., N2 to NH3 or CO2 to CO) in fluid samples (e.g., aqueous samples) without requiring the reactants to be adsorbed to the surface of the hydrogen-terminated diamond.